The present invention relates to a vehicle position and azimuth computing apparatus used in a vehicle navigation system for displaying positions and azimuths of a vehicle and map information on environs of its location.
In a conventional vehicle-mounted navigation system, on-vehicle positions and azimuths are obtained by the use of a speed sensor and an angular velocity sensor, and the on-vehicle positions and azimuths thus obtained are compared with the corresponding positions and azimuths in road data contained in the map information. When a positional difference and an azimuth difference are smaller than predetermined values, respectively, a correction is made so that both the on-vehicle position and on-vehicle azimuth tally with the position and azimuth of a present vehicle position on a road in the map data.
However, there has been a problem that, for instance, when a vehicle is travelling on a new road which is not indicated on a map and so there is no chance to correct its positions and azimuth over a long travelling distance, errors contained in the computed vehicle position and azimuth values accumulate, until a driver of the vehicle would not be able to have correct information on the vehicle's position and azimuth.
To solve this problem, as described in the publications of JP-A-2-112721 (1990) and JP-A-2-212714 (1990), there has been proposed a method of correcting on-vehicle positions by the additional use of an apparatus for obtaining external information, such as a beacon positioned on a road side and a GPS (global positioning system) and thereby compute a present vehicle position. However, the information provided by the beacon or GPS contains only positional information, and therefore the vehicle azimuth cannot be corrected based on this information. Furthermore, another problem is involved in the global positioning system that precision of the position measurement is deteriorated by adverse influences of the reflection by buildings of electromagnetic waves transmitted from the satellites and of a variation of the combination of satellites used in the measurement.